Flame triggered and controlled volumetric ignition

ABSTRACT

The subject matter of this specification can be embodied in, among other things, a method of igniting an air/fuel mixture in an internal combustion engine includes receiving an air/fuel mixture into a pre-combustion chamber, the pre-combustion chamber enclosing a portion of an igniter, igniting the air/fuel mixture in in the pre-combustion chamber with the igniter to produce a flame, directing the flame to eject the pre-combustion chamber through a collection of passages in a wall of the pre-combustion chamber, toward a peripheral wall of a main combustion chamber of the internal combustion engine, igniting, by the flame, air/fuel mixture in the main combustion chamber adjacent the peripheral wall, and then igniting air/fuel mixture in the main combustion chamber in a central region of the main combustion chamber with a propagating flame front of the ignited air/fuel mixture or a portion of the directed flame adjacent the peripheral wall.

TECHNICAL FIELD

This document describes internal combustion engines with ignitionpre-chambers.

BACKGROUND

Engines are commonly operated on a lean air/fuel mixture to reducegeneration of pollutants such as nitrous oxides (NOx). For example,natural gas engines can be run lean to reduce carbon dioxide and NOxemissions, but have high total hydrocarbon emissions (THC), especiallymethane (CH4) in the exhaust, while an oxidation catalyst can reducemost hydrocarbons, no effective methane reduction techniques are knownfor lean burn applications. Some natural gas engines run stoichiometricin order to utilize a three-way catalyst to reduce NOx, CO, and THCemissions, however such solutions historically negatively impact engineefficiency relative to lean burn engines.

SUMMARY

In general, this document describes internal combustion engines withignition pre-chambers.

In one general aspect, a method of igniting an air/fuel mixture in aninternal combustion engine includes receiving an air/fuel mixture into apre-combustion chamber, the pre-combustion chamber enclosing a portionof an igniter, igniting the air/fuel mixture in in the pre-combustionchamber with the igniter to produce a flame, directing the flame toeject the pre-combustion chamber through a collection of passages in awall of the pre-combustion chamber, toward a peripheral wall of a maincombustion chamber of the internal combustion engine, igniting, by theflame, air/fuel mixture in the main combustion chamber adjacent theperipheral wall, and then igniting air/fuel mixture in the maincombustion chamber in a central region of the main combustion chamberwith a propagating flame front of the ignited air/fuel mixture or aportion of the directed flame adjacent the peripheral wall.

Various embodiments can have some, all, or none of the followingfeatures. The main combustion chamber can include a bowl defined in aface of a piston of the internal combustion engine with the face and thebowl at a first end, an elongate cylindrical chamber having acylindrical wall, and a cylinder head at a second end opposite the firstend, the bowl having a wall that is at least partly curved or angled,and a portion of the bowl wall adjacent the ejected flame has anorientation that is obtuse to a trajectory of the ejected flame, andwherein the method further comprises moving the piston proximal a topdead center position wherein a portion of the wall extends into thebowl, and the bowl extends circumferentially around a portion of thewall. All air/fuel mixture received in the pre-combustion chamber can bereceived from the main combustion chamber. Directing the flame to ejectthe pre-combustion chamber through the collection of passages in a wallof the pre-combustion chamber, toward the peripheral wall of the maincombustion chamber of the internal combustion engine can also includeejecting the flame orthogonal to a cylinder wall of the main combustionchamber more laterally than axially. Each of the passages can have awidth, and each of the passages can have a length that is at least anorder of magnitude greater than the width. The method can also includereceiving, from a pressure sensor in the pre-combustion chamber andconfigured to measure fluid pressure in the pre-combustion chamber andthe main combustion chamber, a pressure signal, and adjusting ignitiontiming of the engine based on the pressure signal such that CA50 to CA90is shorter than CA10 to CA50. The method can also include compressing,by the propagating flame front propagating from the peripheral walltoward a central region of the combustion chamber, unburned air/fuelmixture in the central region, and auto-igniting unburned air/fuelmixture in the central region, where later portions of mass fractionburned (MFB) rate are faster than the propagating flame front initialMFB rates. The method can also include receiving, from a pressure sensorin the pre-combustion chamber or main combustion chamber and configuredto measure fluid pressure in the pre-combustion chamber and the maincombustion chamber, a pressure signal, and adjusting ignition timing ofthe engine, in the next combustion cycle after the pressure signal isreceived, based on the pressure signal such that about 85% of the heatrelease (HR) occurs by a predetermined point about 20 degrees after topdead center.

In another general aspect, a system for igniting a mixture in aninternal combustion engine includes an igniter, a pre-combustion chamberenclosing a portion of the igniter, a main combustion chamber having aperipheral wall, and a collection of passages in a wall of thepre-combustion chamber, each passage fluidly connecting thepre-combustion chamber and the main combustion chamber and having a jetaperture configured to direct fluid flow from the passage toward theperipheral wall more laterally than axially.

Various embodiments can include some, all, or none of the followingfeatures. The main combustion chamber can include a bowl defined in aface of a piston of the internal combustion engine with the face and thebowl at a first end, an elongate cylindrical chamber having acylindrical wall, and a cylinder head at a second end opposite the firstend, the bowl having a wall that is at least partly curved or angled,and a portion of the bowl wall adjacent the ejected flame has anorientation that is obtuse to a trajectory of the ejected flame. Thepre-combustion chamber can also include a nose that defines thecollection of passages. The jet apertures of the collection of passagescan be arranged radially. The jet apertures of the collection ofpassages can be arranged to direct flame, ejected from pre-combustionchamber through the collection of passages, orthogonal to a cylinderwall of the engine. Each of the passages can have a width, and each ofthe passages can have a length that is at least an order of magnitudegreater than the width. The pre-combustion chamber can be configured toreceive air/fuel mixture, the igniter can be configured to igniteair/fuel mixture in the pre-combustion chamber to produce a flame, andthe collection of passages can be configured to direct the flame toeject the pre-combustion chamber through the jet apertures in a wall ofthe pre-combustion chamber, toward the peripheral wall of the maincombustion chamber. The peripheral wall of the main combustion chambercan be configured to receive a portion of the flame ejected from the jetapertures, and redirect the portion such that air/fuel mixture in themain combustion chamber proximal the peripheral wall is ignited by theportion, and then air/fuel mixture proximal a central region of the maincombustion chamber is ignited by flame proximal the peripheral wall. Thesystem can also include a pressure sensor in the pre-combustion chamberor main combustion chamber configured to provide a pressure signalrepresentative of a fluid pressure in the pre-combustion chamber and themain combustion chamber. The system can also include a controllerconfigured to adjust activation of the igniter based on the pressuresignal such that CA50 to CA90 is shorter than CA10 to CA50. The systemcan also include a controller configured to adjust activation of theigniter based on the pressure signal such that about 85% of the heatrelease (HR) occurs by about 20 degrees after top dead center.

In another general aspect, an internal combustion engine includes anigniter, an enclosure receiving the igniter, the enclosure defining apre-combustion chamber enclosing a portion of the igniter, a maincombustion chamber having a peripheral wall, and a collection ofpassages in a wall of the pre-combustion chamber, each passage fluidlyconnecting the pre-combustion chamber and the main combustion chamberand having a jet aperture configured to direct fluid flow from thepassage toward the peripheral wall more laterally than axially. The maincombustion chamber can include an elongate cylindrical chamber having acylindrical wall, a bowl defined in a face of a piston at a first end,and a cylinder head at a second end opposite the first end, wherein theperipheral wall is at least partly curved or angled, a portion of theperipheral wall adjacent the jet aperture has an orientation that iscomplimentary to a trajectory of fluid flow based on the configurationof the jet aperture, and a portion of the wall is configured to partlyextend into the main combustion chamber when the piston is near top deadcenter. The peripheral wall can be configured to receive a flame ejectedfrom the jet apertures, and redirect a portion of the flame such thatair/fuel mixture in the main combustion chamber proximal the peripheralwall is ignited by the portion, and then air/fuel mixture proximal acentral region of the main combustion chamber is ignited by flameproximal the peripheral wall. Each of the passages can have a width, andeach of the passages can have a length that is at least an order ofmagnitude greater than the width. The jet apertures of the collection ofpassages can be arranged radially. The jet apertures of the collectionof passages are arranged to direct flame ejected from pre-combustionchamber through the collection of passages orthogonal to a cylinder wallof the engine. The engine can also include a pressure sensor configuredto provide a pressure signal representative of a fluid pressure in thepre-combustion chamber and fluid pressure in the main combustionchamber. The engine can also include a controller configured to adjustactivation of the igniter based on the pressure signal such that CA50 toCA90 is shorter than CA10 to CA50. The engine can also include acontroller configured to adjust activation of the igniter based on thepressure signal such that about 85% of the heat release (HR) occurs byabout 20 degrees after top dead center.

The systems and techniques described here may provide one or more of thefollowing advantages. First, a system can provide a means toconsistently (cycle to cycle), temporally (in time) and spatially (inthe right place in the combustion chamber) generate and controlconditions for auto-ignition in an internal combustion engine, thebenefits of which are (a) faster burn and shorter burn durations (b)operation in the previously “knock-forbidden zone”—i.e. more advancedcombustion phasing or higher compression ratio—by virtue of replacingthe stochastic nature of engine knock (characterized by isolated pocketsof gas in the periphery along the outer edge of the piston near theliner) with a deterministic “group” auto-ignition behavior—whereauto-ignition is achieved without engine knock or pressure oscillationswhich normally characterize engine knocking, thus enabling well knownefficiency improvers—short burn duration, optimal forward combustionphasing, and high compression ratio—even at above normal power densitylevels (BMEP) to achieve new standards in engine efficiency, especiallyfor stoichiometric engines with TWC emissions controls. These benefitsare achieved by virtue of (1) a prechamber with low cycle to cyclevariability which directs the flame jets to the periphery—thus enablinga burn from the outside in flame structure, (2) a piston bowldesign—which has maximal clearance (and minimal squish) in the pistonland region—such that the flame jets can burn without heat losses andquenching to the head and piston, and the prechamber generatessufficient turbulence that squish turbulence is no longer need, andwhich due to the flame from the outside in, creates a collectivicationof the unburned gases into a confined and combined group space, in sucha way that when auto-ignition is triggered, it is a volumetric groupevent as all candidate “auto-ignition zones” will be so closely coupledthat they will all ignite spontaneously at essentially the same time,thus producing a high intensity auto-ignition event that burns up allthe AI candidates, and raises the cylinder pressure at the end of theburn rather than at the beginning (like the delta function of RCCI orHCCI), and (3) cylinder pressure based combustion feedback (RT-CDC)controller and algorithm which enables fast computation of thecombustion metrics such as CA50 (center of combustion), burn duration,and a user defined X2 (MFB-X2) where X2 is set to a number between 50%and 90% of MFB to capture the time at which the auto-ignition eventoccurs and to use fast closed loop control to maintain the user defined“time at which X % of the MFB occurs”, The controlled “bowl volumetricauto-ignition”is triggered by the propagating flame (which burns fromthe outside in towards the bowl) such that the candidate auto-ignitiongases are compressed by the propagating flame heat release andsubsequent pressure rise, which leads to the acceleration of theauto-ignition chemistry. The ideal result is a triangularly shaped heatrelease rate, where the second ½ of the burn rate is faster than at anypoint in the first have, which achieves a fast rise in the cylinderpressure, such that the peak of the heat release is near the end of theburn duration and the peak of the pressure is largely co-incident withthe peak of the heat release rate (which is not true for bell shaped,Gaussian style heat release rates, where the slowest combustion is atthe end of the burn duration.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features andadvantages will be apparent from the description and drawings, and fromthe claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic diagram that shows a partial cross-section of anexample internal combustion engine with an ignition pre-combustionchamber, according to some embodiments.

FIG. 1B shows an enlarged half cross-sectional view of the examplepre-combustion chamber of FIG. 1A.

FIG. 1C shows an enlarged bottom cross-sectional view of the nose ofFIG. 1B.

FIG. 1D shows an enlarged cross-sectional view of the example ignitercarrier of FIG. 1A during compression.

FIG. 1E shows an enlarged half cross-sectional view of another exampleigniter carrier.

FIGS. 2A and 2B are schematic diagrams that show a partial cross-sectionof an example of combustion in the internal combustion engine of FIGS.1A-1E, according to some embodiments.

FIG. 3 shows an example thermal simulation of the propagation of ejectedgasses and combustion of air/fuel mixture within the main combustionchamber.

FIG. 4 shows an example thermal simulation of the propagation ofcombustion of air/fuel mixture within the main combustion chamber.

FIG. 5 is a schematic diagram that shows an example engine system,including a reciprocating engine, a fuel control, and an ignitioncontrol.

FIG. 6 shows two graphs of an example two phase spark ignited combustionevent.

FIG. 7 is a graph that shows an example crossover point.

FIG. 8 is flow chart that shows an example of a process for combustingan air/fuel mixture in an internal combustion engine with apre-combustion chamber, according to some embodiments.

DETAILED DESCRIPTION

This document describes systems and techniques for reducing emissions,increasing power density, and improving efficiency in reciprocatinginternal combustion engines. The concepts described herein encompassboth combustion chamber topologies and control techniques thatfacilitate the combustion improvements. Increasingly restrictive limitson oxides of nitrogen (NOx) levels and desire for low hydrocarbonemissions, especially methane, are driving the change from lean-burn tostoichiometric combustion strategies in order to take advantage ofinexpensive and highly effective catalyst technology. The change tostoichiometric combustion historically limits the power density of anengine due to engine knock caused by higher in-cylinder temperatures. Tosuppress engine knock, exhaust gas recirculation (EGR) rates from 10 to30% are used. While high EGR rates nominally improve brake thermalefficiency (BTE) and reduce exhaust gas temperatures, they also slowdown combustion. To counteract the slow combustion due to high levels ofEGR, a controlled ignition triggered homogeneous charge volumetricignition process is created, resulting in very short burn durations,which can be achieved without the destructive effects of engine knockingor excessive cylinder pressure due to combustion controls, leadingtowards high efficiency gas engines.

In general, engine efficiency is improved by the use of a combustionprocess and engine configuration in which an air/fuel mixture is ignitedin a prechamber and the prechamber turbulent flame reactant jets aredelivered into the center of the combustion chamber or into a dish typepiston shape similar to the way diesel fuel is sprayed into a combustionchamber. The system disclosed herein, however, deviates from knownsystems; for example, since the “end gas” (air/fuel mixture remaininguncombusted near the end of the combustion cycle, typically located nearthe periphery of the cylinder) is usually the source of stochasticauto-ignition and thus the source of engine knocking, the flame jets inthis system are sent horizontally, directly to the “end gas” in order toburn up the heretofore knocking raw ingredients (e.g., like firefighters starting a fire ahead of the flame so it will burn backwardstoward the center) such that the ignited flame jet mixture is ejectedtoward the periphery of the cylinder. The ignited mixture ignites anair/fuel mixture in the main combustion chamber, starting near thecylinder walls first and then propagating inward, away from the wallsand toward the center of the main combustion chamber. With the burn fromthe outside in technique, enabled by the horizontal prechamber jets, the“end gas” becomes trapped in the piston bowl and grouped together suchthat once any portion of it auto-ignites ahead of the inwardlypropagating flame, the entire soup pot of reactants will go off (ignite)all at once. This grouped volumetric auto-ignition generates a singlecombustion event with very fast combustion, in contrast to thehistorical burn from the center out which leads to isolated pocketswhich go off stochastically and without union, leading to the damagingpressure oscillation of knock and to increased heat transfer to the mostvulnerable portion of the piston the piston land. Additionally, inhistorical knock the least cooled portion of the piston (e.g., next tothe rings) gets the extra heating which leads to overheating pistons,which can crack or expand and seize within the cylinder liner. In theburn from the outside in technique, the end gas goes off all at once(e.g., no pressure oscillation waves) and excess heat is transferred tothe piston bowl which can be cooled (e.g., in some embodiments, thepiston bowl can include an oil jet on the back side for cooling and toresist damage to the piston and a thermal barrier coating can also beadded easily to the piston bowl). In some embodiments, engine efficiencycan be increased, for example, by the shorter burn duration (e.g.,second ½ of the mass fraction burned (MFB) takes less time than thefirst ½), the forward combustion phasing, by use of a high compressionratios (e.g., 12:1 to 15:1), and by burning up historically hard to burnCH4, the energy of which can contribute to the heat release andefficiency, and not wasted in the exhaust stream, while catalyzing theremaining emissions, thus achieving zero or near-zero emissions (totalhydrocarbon emissions (THC), NOx, CO), at a point able to reach a CO₂equivalent greenhouse gas (GHG) emission of less than about 500 g/kWh.The concepts herein are especially useful in gaseous fueled engines,including natural gas fueled engines, but are equally applicable toother fuels, including liquid fuels.

FIGS. 1A-1D are schematic diagrams that show partial cross-section viewsof an example of an internal combustion engine 100 with a pre-combustionchamber 110, according to some embodiments. In certain instances, theengine 100 is a four-cycle reciprocating engine, although the conceptsherein are relevant to other configurations of reciprocating engines.The engine 100 includes a cylinder 160 having a center axis 102 and apiston 150 configured for reciprocal movement along the axis 102.

Referring to FIG. 1B, in the illustrated example the pre-combustionchamber 110 is defined within a pre-combustion igniter carrier 101(e.g., an enclosure). The pre-combustion igniter carrier 101 isconfigured to mount in a cylinder head 112. In other instances, thepre-combustion chamber 110 can be formed directly in the cylinder head112 or elsewhere proximate the main combustion chamber.

An igniter 114 (e.g., spark plug such as M10, M12, M14, M18, glow plug,laser igniter, hot surface igniter, or other type of igniter includingdiesel nanopilot) extends partly into the pre-combustion chamber 110 anddefines an ignition location 116 (e.g., spark plug gap, laser focuslocation, hot surface or other ignition location including dieselnanopilot) within the pre-combustion chamber 110. A collection oftubular passages 120 extend from the pre-combustion chamber 110. In theillustrated example, the passages 120 are partly defined within a nose121 (e.g., an end wall) of the pre-combustion chamber 110. In certaininstances, there are four passages 120 equally, circumferentially spacedaround the nose 121, but fewer or more could be provided.

The igniter carrier 101 also includes a pressure sensor 118. Thepressure sensor 118 is in fluid communication with the pre-combustionchamber 110 through a passage 119 defined by the igniter carrier 101. Inuse, the pressure sensor 118 can sense the pressure of gasses within thepre-combustion chamber 110, as will be discussed further in thedescription of FIG. 2B.

The piston 150 is configured for reciprocal movement (as represented byarrow 151) within the cylinder 160. The cylinder 160 has a peripheralwall 162 and is capped with a cylinder head 164. A main combustionchamber 170 is the volume outside of the pre-combustion chamber 110,bounded by the peripheral wall 162 of the cylinder 160, the cylinderhead 164, and the top of the piston 150 (above the piston's compressionrings).

In certain instances, the piston 150 includes an ovoid bowl 171 with aperipheral wall 172 that is curved or angled. The center axis 102 of thecylinder 160 coincides with a center axis of the piston 150 and, incertain instances, the bowl 171 is centered on and wholly symmetricabout that center axis (and in some instances it is not). The collectionof passages 120 extend into the main combustion chamber 170 and proximalto the bowl 171 when the piston 150 is at or near top dead center (TDC).At the ends of the passages 120 proximal the main combustion chamber170, the passages 120 include jet apertures 122 (e.g., openings,nozzles, ejection ports) oriented toward a proximal portion 174 of theperipheral wall 172. The jet apertures 122 are configured to provide asubstantially radial distribution (e.g., spray) of flame ejected fromthe pre-chamber 110 toward the periphery of the cylinder 160, along atrajectory represented by arrows 124, which will be described in moredetail in the descriptions of FIGS. 1C and 2. In some embodiments, thetrajectories 124 are substantially orthogonal to the peripheral wall162. In certain instances, the piston 150 can have a different shape andbe provided without a bowl, for example, being flat, upwardly ordownwardly domed, or have another shape.

The passages 120 include two sections, a major section 123 a and a minorsection 123 b. The major sections 123 a are generally elongate (e.g.,tubular) in shape, each having a width and each having a length, along amajor axis 105 (on which the major section 123 a of the passage iscentered), that is substantially (e.g., an order of magnitude) greaterthan the width (e.g., 2×, 5×, 10×, 50× longer than wide). The major axes105 of the major sections 123 a are parallel to the center axis 102 ofthe cylinder 160. The major sections 123 a are also offset from thelocation of the ignition location 116 (e.g., the main tubular portionsof the passages do not point toward the ignition location 116). Theminor sections 123 b are generally elongate (e.g., tubular) in shape,each having a width and each having a length, along an axis 106. Theaxes 106 extend perpendicular to the major axes 105, the center axis 103of the chamber 110, and the peripheral wall 162.

The jet apertures 122 each have a center axis, and in some instancesthese axes can be oriented substantially orthogonal to the peripheralwall 162 and/or substantially perpendicular to the center axis 102 ofthe cylinder 160. The ratio of length to width, the orientation, andother geometrical properties of the passages 120 are also configured topromote efficient evacuation of the pre-combustion chamber 110. Themajor sections 123 a and the minor sections 123 b have differentlengths, shapes, and aspect ratios. The major sections 123 a aresufficiently long enough (e.g., 2×, 5×, 10×, 50× longer than wide) tocollimate fluid flow around the center axis 105 of the passage 102, andcan have a generally circular cross section (e.g., 1:1 aspect ratio),while the minor sections 123 b can have lengths and aspect ratios (e.g.,2:1, 3:1, 4:1) that promote ejection of flame along the trajectories 124in a pattern that projects a portion of flame across the face 154 to theperipheral wall 162 (e.g., a fan pattern that is substantially co-planarto the face 154.

FIG. 1C shows an enlarged sectional end view of the nose 121. As shownin this view, the passages 120 are offset laterally from the axis 103.As also shown in this view, the passages 120 fluidly connect to the jetapertures 122, and the jet apertures 122 are oriented away from (e.g.,perpendicular to) the axis 103. During pre-combustion, flame is expelledin a radially outward pattern, away from the axis 103 and orthogonal tothe center axis 102 (e.g., and the peripheral wall 162) of the cylinder.

Referring to FIG. 1D, the ratio of length to width, the orientation, andother geometrical properties of the passages 120 is also configured toreduce turbulence of air/fuel mixture near the ignition location 116.The configuration of the passages 120 causes inflow of air/fuel mixture(e.g., during compression strokes), as represented by arrows 104, to thepre-combustion chamber 110 to not flow directly toward the ignitionlocation 116 so incoming air/fuel mixture does not impinge on theignition location 116. For example, the length, width, and aspect ratioof each major section 123 a can be selected to promote a collimated flowof incoming air/fuel mixture, and the orientations of the major sections123 a can be configured so the collimated incoming flow does not alignwith the ignition location 116. As shown in the illustrated example,none of the passages 120 are oriented or otherwise configured to causeincoming flows to impinge on the ignition location 116.

In some embodiments, the inflow 104 can impinge upon a wall of thepre-combustion chamber 110 before propagating into and around theignition location 116. This arrangement places the ignition location 116in a quiescent region of relatively low flow and turbulence, relative tothe higher flow and turbulence that occurs in the trajectories of theflow from the passages 120 during compression. The turbulent areas canhelp purge residuals from crevices (e.g., in a spark plug between theceramic and shell). As such, a flame kernel can develop and grow withinthe ignition location 116 with a reduced likelihood off extinguishment(e.g., blowout) due to turbulence caused by the inflows 104, and thenearby turbulence can help accelerate pre-combustion after the kernelhas grown large enough.

FIG. 1E shows an enlarged half cross-sectional view of another exampleigniter carrier 101′. In some embodiments, the igniter carrier 101′ canbe used in the engine 100 in place of the igniter carrier 101. In theillustrated example, a pre-combustion chamber 110′ is defined within thepre-combustion igniter carrier 101′ (e.g., an enclosure), and thepre-combustion igniter carrier 101′ is configured to mount in thecylinder head 112. In other instances, the pre-combustion chamber 110′can be formed directly in the cylinder head 112 or elsewhere proximatethe main combustion chamber. The pre-combustion chamber 110′ isconfigured to have a cross section that is substantially rectangular,and shaped to create toroidal vortex flow within the chamber 110′ thatis centered around the center axis 103 of the chamber 110′ andcirculates from the top to bottom of the chamber 110′. In someembodiments, the ratio of volume of the pre-combustion chamber 110′ tothe swept volume of the cylinder (V_(pc)/V_(swept)) can be in a range ofabout 800-1200.

The igniter 114 extends partly into the pre-combustion chamber 110′ anddefines an ignition location 116′ (e.g., spark plug gap, laser focuslocation, hot surface or other ignition location including dieselnanopilot) within the pre-combustion chamber 110′. A collection oftubular passages 120′ extend from the pre-combustion chamber 110′through a disk 170 that partly defines a sidewall of the pre-combustionchamber 110′. In some embodiments, the ratio width of the pre-combustionchamber 110′ to the diameter of the disk 170 can be in a range of about1.2 to about 2.0 In certain instances, there are four passages 120′equally, circumferentially spaced around the disk 170, but fewer or more(e.g., 2, 6, 8, 10) could be provided. The tubular passages 120′ aregenerally elongate (e.g., tubular) in shape, each having a width (e.g.,˜1.1 to 1.9 mm diameter) and each having a length, along a major axis105′. In some embodiments, the ratio of chamber volume to disk hole areacan be about 100-200 mm³/mm².

A tubular passage 172 is partly defined within a nose 121′ (e.g., an endwall) of the igniter carrier 101′. The tubular passage 172 extends fromthe disk 170 to a collection of tubular passages 123′ near the end ofthe nose 121′ opposite the chamber 110′. The tubular passage 172 isgenerally elongate in shape, having a width and each having a length,along the chamber center axis 103′, that is substantially (e.g., anorder of magnitude) greater than the width (e.g., 2×, 5×, 10×, 50×longer than wide). The tubular passages 123′ are generally elongate inshape, each having a width and each having a length, along an axis 106′.In the illustrated example, the axes 106′ extend perpendicular to themajor axes 105′, the center axis 103′, and the peripheral wall 162,while in some embodiments the tubular passages may be angled (e.g., +/−about 30 degrees away from perpendicular).

In the illustrated example, the major axes 105′ of the tubular passages120′ are parallel to the center axis 102 of the cylinder 160 and thecenter axis 103 of the chamber 110′. In some embodiments, the tubularpassages 120′ can point to the ignition location 116′. For example, someor all of the tubular passages 120′ can be straight or angled up toabout +30 degrees to promote the removal of hot residuals. In someembodiments, the tubular passages 120′ can be configured with a helicalorientation (e.g., in a helix, twisting circumferentially around thecenter axis 103 to promote a swirl of fluids entering the chamber 110′or the tubular passage 172 through the passages 120′).

The tubular passages 120′ are also offset from the location of theignition location 116′ (e.g., the main tubular portions of the passagesdo not point toward the ignition location 116′). In some embodiments,radial distance from a center axis 103 of the chamber 110′ to the majoraxes 105′ can range from about 2 mm to 4 mm (e.g., radial distance R isa range of about 2 mm<R<R_(rethread)−2 mm).

The nose 121′ and the passage 172 extends into the main combustionchamber 170 and proximal to the bowl 171 when the piston 150 is at ornear top dead center (TDC). The passage 172 is defined to have a channelpassage area that is greater than the total combined area of thepassages 120′, but less than about 1.5 times the total combined area ofthe passages 120′. At the ends of the passages 123′ proximal the maincombustion chamber 170, the passages 123′ include jet apertures 122′(e.g., openings, nozzles, ejection ports) oriented toward the proximalportion 174 of the peripheral wall 172. The jet apertures 122′ areconfigured to provide a substantially radial distribution (e.g., spray)of flame ejected from the pre-chamber 110′ toward the periphery of thecylinder 160, along the trajectory 124.

The ratio of length to width, the orientation, and other geometricalproperties of the passages 120′, the passage 170, the passages 123′, andthe jet apertures 122′ also configured to promote efficient evacuationof the pre-combustion chamber 110′. The passages 120′ are configured todirect fluid flow ignition location 116′, and can have a generallycircular cross section (e.g., 1:1 aspect ratio), while the passages 123′can have lengths and aspect ratios (e.g., 2:1, 3:1, 4:1) that promoteejection of flame along the trajectories 124 in a pattern that projectsa portion of flame across the face 154 to the peripheral wall 162 (e.g.,a fan pattern that is substantially co-planar to the face 154.

In some embodiments, the igniter carrier 101′ can also include apressure sensor (e.g., the pressure sensor 118) in fluid communicationwith the pre-combustion chamber 110′, which can be used to sense thepressure of gasses within the pre-combustion chamber 110′, as will bediscussed further in the description of FIG. 2B.

FIGS. 2A-4 are schematic diagrams that show an example of combustion inthe internal combustion engine 100 of FIG. 1, according to someembodiments. FIGS. 2A and 2B shows an initial stage of combustion in theinternal combustion engine 100.

Referring to FIG. 2B, an air/fuel mixture is provided to thepre-combustion chamber 110 (see, e.g., FIG. 1D). In some embodiments,the pre-combustion chamber 110 is a passive pre-combustion chamber,meaning the entire air/fuel mixture received into the pre-combustionchamber is provided to the pre-combustion chamber 110 from the maincombustion chamber 170. For example, an air and fuel can be providedinto the main combustion chamber 170, premixed by a process orcarburation or fuel injection, and as the piston 150 moves during acompression stroke, a portion of the air/fuel mixture will be pushedinto the pre-combustion chamber 110 through the passages 120. In someembodiments, the pre-combustion chamber 110 is an active pre-combustionchamber or partially active pre-combustion chamber, meaning some or allof the fuel is provided to the pre-combustion chamber 110 directly. Forexample, the pre-combustion chamber 110 can be provided with fuel supply(e.g., an injector) that is in addition to the supply provided to themain combustion chamber.

In the illustrated example, the fuel is natural gas (NG), but in someembodiments other fuels or combinations of fuels can be used, such asdiesel, gasoline, kerosene, hydrogen, biogas, or any other appropriatefuel (e.g., or fuels, in the case of a pilot or dual-fuelconfiguration). In some embodiments, the pre-combustion chamber can beprovided with a different fuel or a different air/fuel mixture from thatprovided to the main combustion chamber. And in some configurations, thepre-combustion chambers 110, 110′ may be fuel enriched with an injectoror gas delivery tube opposite but similarly mounted like the pressuresensor.

The igniter 114 is configured to ignite combustion, forming a flamekernel 200 at the ignition location 116. The kernel 200 ignites theremaining air/fuel mixture and causes the air/fuel mixture to begin tocombust and expand. The increasing pressure of the expanding, combustingmixture forces the combusting mixture out through the passages 120,which fluidly connect the pre-combustion chamber 110 and the maincombustion chamber 170.

As discussed in the description of FIG. 1D, the pre-combustion chamber110 is configured such that the ignition location 116 is located in arelatively quiescent region within the pre-combustion chamber 110, wherethere is relatively low fluid velocity and/or relatively low turbulencecaused by the ingestion of the air/fuel mixture into the pre-combustionchamber 110 and/or combustion of the air/fuel mixture within thepre-combustion chamber. In the illustrated example, the ignitionlocation 116 is located away from the passages 120 where relatively highfluid velocities may develop during compression and/or combustion (e.g.,as expanding gasses escape through the passages 120). By arranging theignition location 116 in a region of low turbulence and/or fluidvelocity, the tendency to extinguish the burgeoning flame kernel can bereduced, which can improve the consistency of the ignition from cycle tocycle.

Referring now to FIG. 2A, as the expanding, combusting gasses travelthrough the passages 120, the jet apertures 122 cause the gasses to beejected away horizontally in some embodiments, but also allows for“tilted” angles from 0 to 30 degrees from the cylinder head deck, from acenter 176 of the main combustion chamber 170 as flaming jets 210. Theflaming jets 210 project to or substantially to the peripheral wall 162of the cylinder 160 above the piston land 150 (e.g., generally along thetrajectories 124 shown in FIG. 1) and into a gap 201 between the pistonland face 154 and the cylinder head 164. As the flaming jets 210progress, some portion is captured by the proximal portions 174 of theperipheral wall 172 of the bowl 171 and some portions may be directedinto the bowl 171. In some embodiments, the piston “squish” region maybe sufficiently proportioned to enable the jet to mostly stay betweenthe cylinder head 164 and the top of the piston land 150. Thepredetermined configuration and arrangement of the passages 120 promotegood combustion stability (e.g., as discussed in the description of FIG.1D) and fast jetting with a high level of diluent (e.g., exhaust gasrecirculation or EGR).

In some embodiments, a thermal barrier coating can be provided on thepiston 150, on the portion of the igniter carrier 101 extending into themain combustion chamber 170, and/or on the walls of the combustionpre-chamber 110 to reduce transfer of heat energy from combustion to thecylinder head 112, the piston 150, and/or the igniter carrier 101, andthen reduce subsequent return of heat energy from these components backto air/fuel mixture in the main combustion chamber 170. For example, byreducing the heating of air/fuel mixture by residual heat in thecombustion chamber, the occurrence of unintended auto-ignition (e.g.,detonation, knock) and thermal run-away can be reduced. The design ofthe engine 100 can also reduce the amount of pumping work needed todeliver diluent.

Referring now to FIG. 3, an example of a thermal simulation of thepropagation of the flaming jets 210 and combustion of air/fuel mixturewithin the main combustion chamber 170 is shown.

The proximal portions 174 of the bowl 171 are formed with angles orcurvatures that are obtuse (e.g., are complimentary to) to thetrajectories of a portion of the flows of the flaming jets 210 in orderto redirect a portion of the flows along the peripheral wall 172. Aportion of the flow of the flaming jets 210 reaches the periphery of thecylinder 160 and ignites air/fuel mixture in the region between the face144 and the cylinder head 164. The peripheral wall 172 redirects anotherportion of the flow of the flaming jets 210 along the periphery of thebowl 171, causing portions of the air/fuel mixture in the bowl 171 nearthe peripheral wall 172 and peripheral wall 162, and away from thecenter 176, to ignite and combust first (e.g., at least partly beforethe air/fuel mixture near the center 176 ignites).

Referring now to FIG. 4, an example thermal simulation of the combustionof air/fuel mixture within the main combustion chamber 170 is shown. Thecombustion that occurs initially near the peripheral wall 172 and theperipheral wall 162 of the cylinder 160 in the gap between the face 154and the cylinder head 164. Both of those regions burn and their flamefronts converge on the bowl 171, where the rising pressure increases theauto-ignition reaction rates—leading to auto-ignition precursors such asOH branching radicals (e.g. H2O2) which when reaching a criticaltemperature and radical population will undergo spontaneous OH branchingthus burning the remaining air/fuel mixture in the bowl 171. Generallyspeaking, the main combustion chamber 170 burns from the outside in(e.g., propagating away from the peripheral wall 162 and the gap), andany uncombusted portions 410 of air/fuel mixture that has the potentialto unintentionally auto ignite is collected in the bowl, where it isintentionally trapped and compressed by the propagating flame and ispurposely auto-ignited, and thus burns rather quickly so it has littleopportunity for traditional stochastic islands of auto-ignition whichlead to knocking combustion, or if it does auto ignite it does sointentionally and all at once such it is not substantially detrimentaldue to the lack of any ringing in the combustion chamber thathistorically causes the destructive effects of stochastic uncontrolledauto-ignition and knock.

The main combustion chamber 170 has a predetermined shape that promotesthe propagation of the flaming jets 210 directed about the periphery ofthe main combustion chamber, to ignite combustion near the peripheralwall 162 generally first so combustion near the center 176 happens as agenerally secondary event. The shape of the main combustion chamber 170is also predetermined in part to increase the efficiency andcontrollability of the combustion process. For example, the combustioncan be caused to occur faster, especially in the second half of the heatrelease cycle. In the illustrated examples, the engine 100 is configuredsuch that the angle span between second half of combustion, historicallythe slowest rate due to expanding piston, fuel near the walls, lowertemperature and lower turbulence, CA50 (i.e., the crank angle where 50%mass fraction of the air/fuel mixture introduced into the combustionchamber is burned) and CA90 (90% mass fraction burned) is faster thanthe historically fast part of the combustion from CA10 (10% massfraction burned) and CA50 (50% mass fraction burned). In other words,the engine 100 is configured to cause a large amount of the combustionto happen during a relatively short portion of the combustion cycle, andthat short portion happens relatively late in the combustion cycle.(e.g., combustion happens faster during the last half of the cycle).

The combustion from the periphery of the cylinder 160 inward toward thecenter of the main combustion chamber helps control where auto-ignitionoccurs (i.e., toward the center of the main combustion chamber) so thatefficiency and engine lifespan can be increased. The shape of the pistonbowl 171, although optional, additionally helps control whereauto-ignition occurs. For example, engine knock can damage pistons andcylinder walls (e.g., detonation near walls causes incremental damagethat can lead to engine malfunction and/or failure), and in previousdesigns, knock is remedied or avoided by lowering compression and/or byselecting less favorable air/fuel ratios or retarding the combustionphasing (CA50). However, the design of the engine 100 promotes acontrolled burn of the fuel near the periphery first, such that unburnedfuel is concentrated near the center 176 at the time in the pistonstroke when the combustion chamber pressures and temperatures are highand most conducive to unwanted auto-ignition, such that if and whenauto-ignition does occur it happens near the center 176, away from theperipheral wall 172, and at a time and location near where the fuelwould be intentionally ignited anyway. In other words, the regions nearthe peripheral walls 162 and 172 are combusted early so they cannotunintentionally auto-ignite later.

FIG. 5 is a schematic diagram that shows an example engine controlsystem 500 for a reciprocating engine. The system 500 is an example ofhow the various components of FIGS. 1A-4 can be brought together withadditional components for air, fuel, sensing, and control to form acomprehensive system that can be used to provide intelligent, pressurebased control of an engine with reduced emissions, reduced heattransfer, and increased efficiency through combustion strategy andcontrol, such as the engine 100.

A controller 501, such as an Engine Control Module (ECM), is ahysteretic current or voltage controller used to control the actuationor an air flow control valve 510 and a fluid admission valve 550 (e.g.,a gas mixer). The fluid admission valve 550 is actuated by thecontroller 501 to control the flow of natural gas fuel or otherappropriate fuel from a fuel conduit 555 to an air intake 543 (e.g., aninlet). The controller 501 is also used to control an exhaust gasrecycle (EGR) valve 565 to control the flow of exhaust gasses from anoutlet 544 though an EGR passage 560 to the air intake 543. In someembodiments, the EGR passage 560 can be configured with a venturi jetpump to draw the recycled exhaust gasses into the intake. By controllingthe air flow, fluid admission valve 550 and the EGR valve 565, thecontroller 501 can control the amount of combustible natural gas that issupplied to the air intake 543. In other words, the controller 501 cancontrol the fluid admission valve 550 so the fuel mixture provided tothe main combustion chamber 170 has a controlled, predetermined air/fuelratio. In some embodiments, the air/fuel ratio can be set nominally andvery precisely lamba 1.0+/−0.01 (e.g., so that it feeds an appropriatemixture to a downstream catalytic converter).

The controller 501 also controls actuation of an ignition module 505.The ignition module 505 operates based on a signal from the controller501 to energize the igniter 114 and ignite a combustion process (e.g.,as discussed in the descriptions of FIGS. 3 and 4).

Combustion of fuel generates pressure within the pre-combustion chamber110 and then by flame jets the main combustion chamber 170. Pressurewithin the pre-combustion chamber 110 and the main combustion chamber170 is sensed by the pressure sensor 118, and pressure signals from thepressure sensor 118 are read and processed by the controller 501. Insome embodiments, the pressure can be sensed directly from the maincombustion chamber. In some embodiments, the system 500 can include areal-time combustion and diagnostics control (RT-CDC) system. The RT-CDCsystem can be used to monitor the combustion metrics and feed them tothe controller 501 to use as smart sensor information for closed-loopcontrol. In some examples, the center of combustion (CA50) can bemonitored and sent to the controller 501, which in turn can beconfigured to adjust ignition timing to maintain a target CA value(e.g., CA50).

As such, the controller 501 is configured to control the timing of theignition in real-time or near real-time, based on one or more measuredvariables such as pre-combustion pressure, main combustion pressure,crank position, air/fuel ratio, engine load, available oxygen (e.g., O2,elevation), engine speed (RPMs), temperature, fuel quality, compressionratio, EGR ratio, and any other appropriate variable of enginecombustion. The controller 501 controls ignition to control the timingof the flaming jets 210 (as monitored by the pressure sensor 118) tocontrol the combustion of fuel in the main combustion chamber 170 (asmonitored by the pressure sensor 118) to achieve efficient combustion.The controller 501 can adjust the ignition timing and air/fuel mixtureto shift the center of combustion (CA50) to optimize combustion. Thecontroller can also use auto-ignition metrics to control the degree ofauto-ignition, such as the difference between the 10-50 MFB and the50-90 MFB ratios, the location of X2 MFB (nominally X2 is set to between70% and 85% of the MFB), and adjust controllable factors tointentionally and consistently induce auto-ignition in the bowl.

During the combustion stroke, the controller 501 identifies a referenceevent such as TDC or a crank offset from TDC based on an engine cranksensor, or based on actuation of the ignition module 505. For example,as the air/fuel mixture in the pre-combustion chamber 110 combusts, gaspressures increase and then diminish in a wave. By adjusting the timingof the ignition, the controller 501 can control the timing ofpre-chamber pressure and/or heat release rate (HRR) peak to control thetiming of ejection of combusting gasses into the main combustion chamber170. Using the pressure sensor 118, the controller 501 can confirm thatthe ejection of combusting gasses into the main combustion chamber 170is occurring as expected, and if not, advance or retard the timing ofthe ignition signal to compensate for any lag/lead in the ejection ofcombusting gasses. In some embodiments, the ignition timing can beadjusted to cause the resulting ejection of combusting gasses to occurin a specified window before TDC (e.g., from about 3 degrees before TDCto about 5 degrees after TDC).

The controller 501 is also configured to take remedial measures toprevent engine damage when engine knock is identified (e.g., alterair/fuel ratio, alter ignition timing, reduce engine load, alter fuelinjection timing, increase EGR rates). The controller 501 can also beconfigured to take other steps in the absence of detected engine knock.For example, the controller 501 may determine that more aggressiveengine parameters can be applied in order to economize the consumptionof fuel by the engine and/or to reduce emissions.

The controller 501 can be used for the operations described hereinaccording to one implementation. The controller 501 includes a processor502, a memory 504, a storage device 506, and switching controller 508.The processor 502 is capable of processing instructions for executionwithin the system 500. In one implementation, the processor 502 can be afield-programmable gate array (FPGA) processor. For example, with theadvent of very fast FPGAs, it is possible to look carefully at theswitching controller 508 logic and detect very small variations incurrent and voltage waveforms at very fast clock rates.

In another implementation, the processor 502 can be a single-threadedprocessor. In another implementation, the processor 502 can be amulti-threaded processor. In some implementations, the processor 502 canbe capable of processing instructions stored in the memory 504 or on thestorage device 506 to collect information from, and provide controlsignals to, the ignition module 505.

The memory 504 stores information within the controller 501. In someimplementations, the memory 504 can be a computer-readable medium. Insome implementations, the memory 504 can be a volatile memory unit. Insome implementations, the memory 504 can be a non-volatile memory unit.

The storage device 506 is capable of providing mass storage for thesystem 100. In one implementation, the storage device 506 is acomputer-readable medium. In various different implementations, thestorage device 506 may be non-volatile information storage unit (e.g.,FLASH memory).

The switching controller 508 provides control signal output operationsfor the controller 501. The switching controller 508 provides actuationcontrol signals (e.g., pulse width modulated, PWM, driver signals) thatactivate the ignition module 505 and the fluid admission valve 550. Forexample, the switching controller 508 can include field effecttransistors (FETs) or other switching devices that can convert alogic-level signal from the processor 502 to a current and/or voltagewaveform with sufficient power to drive a coil of the ignition module505. In another implementation, the switching controller 508 can providedigital or analog signals configured to control servo valves within thefluid admission valve 550.

The features described herein can be implemented in digital electroniccircuitry, or in computer hardware, firmware, software, or incombinations of them. The apparatus can be implemented in a computerprogram product tangibly embodied in an information carrier, e.g., in amachine-readable storage device for execution by a programmableprocessor; and method steps can be performed by a programmable processorexecuting a program of instructions to perform functions of thedescribed implementations by operating on input data and generatingoutput. The described features can be implemented advantageously in oneor more computer programs that are executable on a programmable systemincluding at least one programmable processor coupled to receive dataand instructions from, and to transmit data and instructions to, a datastorage system, at least one input device, and at least one outputdevice. A computer program is a set of instructions that can be used,directly or indirectly, in a computer to perform a certain activity orbring about a certain result. A computer program can be written in anyform of programming language, including compiled or interpretedlanguages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment.

Suitable processors for the execution of a program of instructionsinclude, by way of example, both general and special purposemicroprocessors, and the sole processor or one of multiple processors ofany kind of computer. Generally, a processor will receive instructionsand data from a read-only memory or a random access memory or both. Theessential elements of a computer are a processor for executinginstructions and one or more memories for storing instructions and data.Generally, a computer will also include, or be operatively coupled tocommunicate with, one or more mass storage devices for storing datafiles; such devices include magnetic disks, such as internal hard disksand removable disks; magneto-optical disks; and optical disks. Storagedevices suitable for tangibly embodying computer program instructionsand data include all forms of non-volatile memory, including by way ofexample semiconductor memory devices, such as EPROM, EEPROM, and flashmemory devices; magnetic disks such as internal hard disks and removabledisks; and magneto-optical disks. The processor and the memory can besupplemented by, or incorporated in, ASICs (application-specificintegrated circuits).

Although the examples shown in FIGS. 1A-5 depict cross-sectional viewsof a single cylinder 160, piston 150, and igniter carrier 101, theengine 100 and the system 500 can have more than one identical cylinder,piston, and pre-combustion chamber assembly. For example, the engine 100can include 2, 4, 6, 8 or more cylinders 160 and pistons 150, each witha pre-igniter carrier 101 having a pre-combustion chamber 110.

FIG. 6 shows a graph 610 and a graph 650 of an example two phase sparkignited combustion of a premixed natural gas, EGR, and air mixture.While auto-ignition of end gas is historically equated with knockingcombustion, in certain instances, the concepts herein can generateconditions for and achieve auto-ignition of end gasses without knockingcombustion.

In FIG. 6, a graph 610 shows an example of cylinder pressure (bar) andcrank angle (degrees) according to the concepts herein, and includes apressure trace 612 and a motored, polytropic curve 614. A graph 650shows example traces of an example heat release rate trace 652 (HRR,kj/m³/deg) and an integral (cumulative or total) heat release trace 654(HR, kj/m³) as functions of crank angle. In some implementations, theexample controller 501 of FIG. 5 can be configured to measure, e.g., viainput from (among other inputs) an in-cylinder pressure sensor, asdiscussed above, and analyze such information sensed from the engine100, the pre-combustion igniter carrier 101, and/or the pre-combustionigniter carrier 101′ of FIGS. 1A-5.

The HRR trace 652 is not typical of conventional combustion. Aconventional HRR combustion curve would have a heat release rate curvethat resembles a bell curve, wherein the peak of the HRR is near thecentroid of the integral (CA50). In contrast, the disclosed combustionchamber topology and control techniques can have a HRR trace 652 with apeaked/triangular shape that rises until the combustion runs out of fuelto burn, then drops off sharply. This combustion pattern is a result ofthe “outside-in” controlled, flame propagated volumetric auto-ignitionof the fuel, starting near the periphery of the main combustion chamber(e.g., due to the controlled timing of the pre-combustion ignition andthe subsequent jetting of the pre-combustion gasses toward the peripheryof the main combustion chamber), and propagating inward toward thecenter of the main combustion chamber (e.g., collecting and compressingthe unburned air/fuel as the flame front progresses inward).

As described, this is an example where the last portion of the HRR(around 15 degrees after top dead center (ATDC), as highlighted by line660) is much faster than the center of combustion HRR (around 10 degreesATDC, as highlighted by line 662). Additionally, the integral HR trace654 shows an upward concavity. The pressure trace 612, while showing apressure rise due to auto-ignition of end gasses, does not show anypressure ripple or ringing associated with engine knock, and the peak ofthe pressure curve is near or slightly after the peak of thetriangularly shaped HRR.

Typically, without the combustion control provided by the controller501, this would be considered an unsafe operating condition on the edgeof being out of control, and would be called un-controlled combustion.However, in the example shown, pressure based combustion feedback in theloop of the controller 501 maintains stable and phase controlled end gascombustion by adjusting the spark timing for each cycle.

However, with the combustion control provided by the controller 501 forthe engine 500, the combustion process control variable can be movedcloser to the end of the combustion cycle (e.g., by controlling engineparameters to control the location of CA75-85 or where peak HRR occurs),and to control the shutdown of the heat release based on the peak. Insome implementations, the rate of heat release is possibly accelerateddue to auto-ignition. The combustion control provided by the controller501 for the engine 500, can alter the ignition timing such that gasexpansion due to combustion starts during the constant volume portion ofpiston stroke, and peak HRR occurs at a predetermined crank angle (e.g.,15-20 degrees ATDC, although this target can change depending on thespecific application, engine, loading, speed, and use case) as afunction of mechanical expansion ratio for efficiency. For example, incertain instances, the controller 501 can be configured to identify thesecond peak in the HRR curve (e.g., the first peak near TDC is due toinitial ignition in the prechamber and the peak 653 at 660, in FIG. 6,is due to combustion in the main combustion chamber), and in the nextcycle of the cylinder, control engine parameters to shift the locationof the second peak relative to piston position and affect, and incertain instances, optimize the efficiency of the combustion cycle inproducing engine torque and power. In certain instances, the controller501 can control engine parameters, including ignition timing, to controlCA80 to be 15 degrees ATDC. The particular tuning and timing provided bythe controller 501 (whether it be controlling the location of CA75,CA80, CA85 or another value and whether the target position be 15degrees ATDC, 20 degrees ATDC or another value) can be determinedautomatically by the controller 501, or through simulation/modelling orexperimentation and then provided to the controller 501.

The benefits of controlling the auto-ignition of end gasses are many,for example shorter burn duration, pressure rise after center ofcombustion, and quick burn up of the otherwise hard to burn gases in theend gas. The phenomena of auto-ignition of end gasses where in the bulkof candidate end gas goes off all at once or volumetrically is similarto the phenomena in HCCI and RCCI and their benefits, namely thesubstantial elimination of the propagating flame in favor of volumetricignition.

FIG. 7 is a graph 700 that shows an example crossover point near 12.5ATDC (represented by line 702), where both halves of an examplecombustion burn rate are approximately equal in burn duration (BD)(e.g., [10-50] BD=[50-90] BD).

The graph 700 shows that, when starting on the right side (e.g.,“retarded” combustion) and moving left (e.g., “advance” combustion) the[50-90] burn duration (represented by trace 730), which starts outlonger than the [10-50] BD (represented by trace 720), the crossoverpoint 702 at about 12.5 CA50, where the [50-90] BD becomes shorter andfaster than the [10-50] BD, and provides a clear indications ofauto-ignition in end gasses. In some implementations, the examplecontroller 501 of FIG. 5 can be configured to sense, identify, andrespond to detected auto-ignition of end gasses in real time or nearreal time, e.g. during the same combustion cycle the auto-ignition isidentified in.

The graph 700 shows that the normal relationship that second half of theburn duration (e.g., [50-90] BD) is slower than the first half, as mightbe expected for normal gas engine combustion. However, moving from rightto left it can be seen that at the cross-over point 702, where thesecond half of the burn duration (e.g., [50-90] BD) is approximatelyequal in duration as the first half (e.g., [10-50] BD), both halves haveapproximately same speed. When combustion phasing is further advanced,the second half of the combustion is now shorter than first half. Thisis the regime where auto-ignition of end gasses occurs, which serves toaccomplish this unusual phenomenon. In some severe cases, the secondhalf of the combustion is approximately ½ the duration of the firsthalf.

Combustion and other measurable engine operational metrics (e.g., suchas those shown as the example traces of FIGS. 5 and 6) can be measuredby the controller 501, to identify patterns and trends to determinecharacteristics of combustion, and the controller 501 can modifyoperation of the engine system 500 based on such characteristics,patterns, and trends. For example, the HRR trace 652 exhibits anidentifiable peaked triangular or tent-shaped characteristic having apeak 653. In another example, the HRR trace 652 exhibits an after centerof combustion (CA50) that is greater than the HRR before center ofcombustion, in which HRR does not diminish like normal combustion thatbecomes “resource limited” (e.g., temperature, turbulence, fuel nearliner and in crevice area). In another example, the controller 501 canquantify the [50-90] Burn Duration as being greater than or equal to the[10-50] Burn Duration. In another example, the upturned slope on theintegrated total heat release curve after 50% MFB (e.g., ca50 or CoC)can be identified by the controller 501 and used as strong evidence ofauto-ignition of end gasses.

The controller 501 is configured to sense combustion characteristics,such as those already discussed, and alter ignition timing (or EGRrates) in order to modify the timing of combustion relative to crankangle in order to modify the combustion process. For another example,the location of peak pressure (e.g., in trace 612) is approximately atthe same location (or after) as the peak/end of the triangular burn.

The trace 612 is not what would be seen as a result of normal/typicalcombustion; during typical combustion, the peak pressure occurs near thecenter of combustion, not at the 90% MFB point as it is in the trace612. In short, the system 500 can be configured to analyze combustioninformation in order to protect the system 500 and its geometry andcontrol, and also cause the phenomena in which the second half burn timeis shorter than first half burn time. In some examples, these outcomescan be verified experimentally (e.g., disassemble and inspect and/orpressure trace and heat release). While the distinction before and after50% MFB is used in this example, in some embodiments, it would bepossible to have a user defined ratio of fuel burned “via flamepropagation” and “via auto-ignition” where another number than 50% couldbe used, i.e. 30% fuel burned by flame propagation which triggers theremaining 70% to be burned by auto-ignition. In the extreme, where 90%or more of the fuel is burned by auto-ignition, the flame would be onlya minor trigger. The higher the compression ratio, the greater thedegree of auto-ignition fraction can be achieved. And in the limit wherea delta function of apparently total volumetric ignition would be HCCIor RCCI combustion. In any case, not only the timing of, but also theratio of auto-ignition to flame propagation can be sensed andcontrolled.

FIG. 8 is flow chart that shows an example of a process 800 forcombusting an air/fuel mixture in an internal combustion engine with apre-combustion chamber, according to some embodiments. In someembodiments, the process 800 can be performed by the engine 100 of FIGS.1A-4, or the system 500 of FIG. 5.

At 810 an air/fuel mixture is received into a pre-combustion chamber,the pre-combustion chamber enclosing a portion of an igniter. In someembodiments, the process 800 can include receiving air/fuel mixture fromthe main combustion chamber. For example, air and fuel provided to themain combustion chamber 170 can be pushed into the pre-combustionchamber 110 when the piston 150 is on a compression stroke, so calledpassive prechamber. In some embodiments, the pre-combustion chamber maybe fitted with a dedicated enrichment or scavenging injector (e.g.,sometimes called an “active prechamber”).

In some embodiments, the piston can be configured with a bowl and theperipheral wall can be at least partly curved or angled, and a portionof the peripheral wall adjacent the ejected flame can have anorientation that is complimentary to a trajectory of the ejected flame.For example, peripheral wall 172 is formed as a bowl and the proximalportions 174 have a slope that is less than orthogonal to thetrajectories 124.

In some embodiments, the bowl can be defined in the face of the pistonof the internal combustion engine, and the process 600 can also includemoving the piston proximal a top dead center position such that the noseextends at least partly into the bowl, and the bowl extendscircumferentially around a portion of the nose. For example, when thepiston 150 is moved near TDC, the nose 121 and the passages 120 definedwithin the nose 121 extend partly into the main combustion chamber 170.

In some embodiments, the main combustion chamber can also include anelongate cylindrical chamber having a cylindrical wall, the face and thebowl at a first end, and a cylinder head at a second end opposite thefirst end. For example, the main combustion chamber 170 can be definedby the peripheral wall 172, the face 154, the cylinder head 164, theperipheral wall 162 of the cylinder 160, and piston rings (not shown)that seal the piston 150 against the peripheral wall 162.

Historically, techniques for speeding up combustion with EGR addedturbulence to swirl or tumble an air/fuel mixture at the intake valves,and then “squish” the mixture between the top of the piston land and thecylinder head creating squish, which jets the mixture out of the pistonland region into the bowl where the turbulence in the bowl leads to fastcombustion. In the illustrated embodiment, no such squish-generatedturbulence is required, so a quiescent low swirl intake system and lowsquish can be used because the pre-combustion chamber turbulent jetsgenerate the turbulence (e.g., much like diesel spray plumes generatetheir own turbulence). Thus the illustrated examples could have a largesquish region gap specification.

At 820, the air/fuel mixture in in the pre-combustion chamber is ignitedto produce a flame jet. For example, the igniter 114 can be energized tocreate an ignition that ignites the air/fuel mixture in thepre-combustion chamber 110.

At 830 the flame is directed to eject the pre-combustion chamber througha collection of passages in a wall of the pre-combustion chamber, towarda peripheral wall of a main combustion chamber of the internalcombustion engine. In some embodiments, the flame is ejected from thepre-combustion chamber through a collection of passages using pressurefrom combustion in the pre-combustion chamber. In some embodiments,directing the flame to eject the pre-combustion chamber through thecollection of passages in a wall of the pre-combustion chamber, towardthe peripheral wall of the main combustion chamber of the internalcombustion engine can include ejecting the flame toward the peripheralwall in a radial pattern. In some embodiments, directing the flame toeject the pre-combustion chamber through the collection of passages in awall of the pre-combustion chamber, toward the peripheral wall of themain combustion chamber of the internal combustion engine can includeejecting the flame orthogonal to a cylinder wall of the engine. Forexample, as illustrated in FIG. 2A, pressures created within thepre-combustion chamber 110 can drive fluids in the pre-combustionchamber 110 to escape through the passages 120. The jet apertures 122direct the escaping combusting gasses substantially orthogonal to theperipheral wall 162 and the proximal portion 174 of the peripheral wall172.

In some embodiments, each of the passages can have a width, and each ofthe passages can have a length that is at least an order of magnitudegreater than the width. For example, the passages 120 are generallytubular in shape, each being substantially longer (e.g., 2×, 5×, 10×,50×) than their width. The ratio of length to width and othergeometrical properties of the passages 120 can be selected to promoteefficient evacuation of the pre-combustion chamber 110 and jetting ofejected combusting gasses into the main combustion chamber 170.

At 840, the flame ignites the air/fuel mixture in the main combustionchamber adjacent the peripheral wall. For example, as illustrated inFIG. 3, the combusting gasses ejected from the jet apertures 122 travelalong the peripheral wall 172, igniting additional air/fuel mixtureproximal the peripheral wall 172.

At 850, the air/fuel mixture in the main combustion chamber in a centralregion of the main combustion chamber is ignited with the ignitedair/fuel mixture adjacent the peripheral wall. For example, asillustrated in FIG. 4, the combustion that occurs initially near theperipheral wall 172 propagates centrally inward, igniting thestill-unburned air/fuel mixture near the center 176.

In some embodiments, the process 800 can also include receiving, from apressure sensor configured to measure fluid pressure in thepre-combustion chamber, a pressure signal, and adjusting ignition timingof the engine based on the pressure signal. For example, the examplecontroller 501 of FIG. 5 can receive pressure signals from the pressuresensor 118, and adjust the ignition timing of the igniter 114 based onpatterns and trends within the pressure signals that can be identifiedby the controller 501.

While most of the examples discussed in this document describe systemsin which the controller configured to adjust activation of the igniterbased on the pressure signal such that CA50 to CA90 is shorter than CA10to CA50, the controller can be configured to control other combustionpatterns. In some implementations, the controller can be configured suchthat the “later” burn rates are faster than the previous burn rates. Forexample, the controller can be configured more aggressively, such as 10%propagating and 90% auto-ignition. In another example, the controllercan be configured with more relaxed parameters, such as 90% MFBpropagating flame and 10% auto-ignition.

Although a few implementations have been described in detail above,other modifications are possible. For example, the logic flows depictedin the figures do not require the particular order shown, or sequentialorder, to achieve desirable results. In addition, other steps may beprovided, or steps may be eliminated, from the described flows, andother components may be added to, or removed from, the describedsystems. Accordingly, other implementations are within the scope of thefollowing claims.

What is claimed is:
 1. A method of igniting an air/fuel mixture in aninternal combustion engine, the method comprising: receiving an air/fuelmixture into a pre-combustion chamber, the pre-combustion chamberenclosing a portion of an igniter; igniting the air/fuel mixture in inthe pre-combustion chamber with the igniter to produce a flame, thepre-combustion chamber having a wall and a plurality of passages in thewall proximal a cylinder head; moving a piston proximal a top deadcenter position wherein a portion of the wall extends into an ovoid bowldefined in a face of the piston of the internal combustion engine withthe face and the ovoid bowl at a first end and the cylinder head at asecond end opposite the first end, the ovoid bowl having an ovoid bowlwall that is at least partly curved or angled to define a center of theovoid bowl, and a portion of the ovoid bowl wall adjacent the face isobtuse to the face, and a portion of the ovoid bowl extendscircumferentially around a portion of the wall, and defining a gapbetween the cylinder head, the face of the piston, and a peripheral wallof a main combustion chamber of the internal combustion engine;directing the flame to eject the pre-combustion chamber through theplurality of passages in the wall of the pre-combustion chamber proximalto the cylinder head away from the center of the ovoid bowl, along aperiphery of the cylinder head, toward the gap and the portion of theovoid bowl wall adjacent the face; then igniting, by the ejected flame,air/fuel mixture in the main combustion chamber adjacent the ovoid bowlwall; and then igniting air/fuel mixture in the main combustion chamberin a central region of the main combustion chamber with a propagatingflame front of the ignited air/fuel mixture or a portion of the directedflame adjacent the ovoid bowl wall.
 2. The method of claim 1, whereinthe main combustion chamber comprises the ovoid bowl, an elongatecylindrical chamber having a cylindrical wall, and the cylinder head,and a portion of the ovoid bowl wall adjacent the ejected flame has anorientation that is obtuse to a trajectory of the ejected flame.
 3. Themethod of claim 1, wherein all air/fuel mixture received in thepre-combustion chamber is received from the main combustion chamber. 4.The method of claim 1, wherein directing the flame to eject thepre-combustion chamber through the plurality of passages in the wall ofthe pre-combustion chamber proximal to the cylinder head, toward the gapand the portion of the ovoid bowl wall adjacent the face furthercomprises ejecting the flame orthogonal to a cylinder wall of the maincombustion chamber more laterally than axially.
 5. The method of claim1, wherein each of the passages has a width, and each of the passageshas a length that is at least an order of magnitude greater than thewidth.
 6. The method of claim 1, further comprising: receiving, from apressure sensor in the pre-combustion chamber and configured to measurefluid pressure in the pre-combustion chamber and the main combustionchamber, a pressure signal; and adjusting ignition timing of the enginebased on the pressure signal such that CA50 to CA90 is shorter than CA10to CA50.
 7. The method of claim 6, further comprising: compressing, bythe propagating flame front propagating from the peripheral wall towarda central region of the combustion chamber, unburned air/fuel mixture inthe central region; and then auto-igniting unburned air/fuel mixture inthe central region; wherein later portions of mass fraction burned (MFB)rate are faster than initial MFB rates of the propagating flame front.8. The method of claim 1, further comprising: receiving, from a pressuresensor in the pre-combustion chamber or main combustion chamber andconfigured to measure fluid pressure in the pre-combustion chamber andthe main combustion chamber, a pressure signal; and adjusting ignitiontiming of the engine, in another combustion cycle after the pressuresignal is received, based on the pressure signal such that about 85% ofheat release (HR) occurs by a predetermined point about 20 degrees aftertop dead center.
 9. A system for igniting a mixture in an internalcombustion engine, the system comprising: an igniter; a main combustionchamber having a peripheral wall defining a center axis and comprisingan elongate cylindrical chamber having a cylindrical wall, a piston ofthe internal combustion engine with a face at a first end, a cylinderhead at a second end opposite the first end, an ovoid bowl defined inthe face of the piston and having an ovoid bowl wall that is at leastpartly curved or angled defining a center of the ovoid bowl, and aportion of the ovoid bowl wall adjacent the face is obtuse to the face,and a gap defined between the cylinder head, the face of the piston, andthe cylindrical wall; a pre-combustion chamber centered on the centeraxis and enclosing a portion of the igniter; a plurality of passages ina wall of the pre-combustion chamber, each passage fluidly connectingthe pre-combustion chamber and the main combustion chamber and having ajet aperture proximal to the cylinder head away from the center of theovoid bowl and configured to direct fluid flow from the passage along aperiphery of the cylinder head toward the gap and the peripheral wallmore laterally than axially, wherein a portion of the wall of thepre-combustion chamber extends into the ovoid bowl, and the portion ofthe ovoid bowl extends circumferentially around a portion of the wall ofthe pre-combustion chamber when the piston is configured proximal a topdead center position.
 10. The system of claim 9, wherein a portion ofthe ovoid bowl wall adjacent the directed fluid flow has an orientationthat is obtuse to a trajectory of the directed fluid flow.
 11. Thesystem of claim 9, wherein the pre-combustion chamber further comprisesa nose that defines the plurality of passages.
 12. The system of claim9, wherein the jet apertures of the plurality of passages are arrangedradially.
 13. The system of claim 9, wherein the jet apertures of theplurality of passages are arranged to direct fluid flow, ejected frompre-combustion chamber through the plurality of passages, orthogonal tothe cylindrical wall.
 14. The system of claim 9, wherein each of thepassages has a width, and each of the passages has a length that is atleast an order of magnitude greater than the width.
 15. The system ofclaim 9, wherein: the pre-combustion chamber is configured to receiveair/fuel mixture; the igniter is configured to ignite air/fuel mixturein the pre-combustion chamber to produce a flame; and the plurality ofpassages are configured to direct the flame to eject the pre-combustionchamber through the jet apertures in a wall of the pre-combustionchamber, proximal to the cylinder head, away from the center of theovoid bowl, and toward the cylindrical wall of the main combustionchamber.
 16. The system of claim 9, wherein the ovoid bowl wall of themain combustion chamber is configured to receive a portion of fluid flowdirected from the jet apertures, and redirect the portion such thatair/fuel mixture in the main combustion chamber proximal the ovoid bowlwall is ignited by the portion, and then air/fuel mixture proximal acentral region of the main combustion chamber is ignited by flameproximal the peripheral wall.
 17. The system of claim 9, furthercomprising a pressure sensor in the pre-combustion chamber or maincombustion chamber configured to provide a pressure signalrepresentative of a fluid pressure in the pre-combustion chamber and themain combustion chamber.
 18. The system of claim 17, further comprisinga controller configured to adjust activation of the igniter based on thepressure signal such that CA50 to CA90 is shorter than CA10 to CA50. 19.The system of claim 17, further comprising a controller configured toadjust activation of the igniter based on the pressure signal such thatabout 85% of heat release (HR) occurs by about 20 degrees after top deadcenter.
 20. An internal combustion engine comprising: an igniter; a maincombustion chamber having a peripheral wall defining a center axis andcomprising an elongate cylindrical chamber having a cylindrical wall, apiston of the internal combustion engine with a face at a first end, acylinder head at a second end opposite the first end, an ovoid bowldefined in the face of the piston and having an ovoid bowl wall that isat least partly curved or angled defining a center of the ovoid bowl,and a portion of the ovoid bowl wall adjacent the face is obtuse to theface, and a gap defined between the cylinder head, the face of thepiston, and the cylindrical wall; an enclosure receiving the igniter,the enclosure defining a pre-combustion chamber centered on the centeraxis and enclosing a portion of the igniter; and a plurality of passagesin a wall of the pre-combustion chamber, each passage fluidly connectingthe pre-combustion chamber and the main combustion chamber and having ajet aperture proximal to the cylinder head away from the center of theovoid bowl and configured to direct fluid flow from the passage along aperiphery of the cylinder head toward the gap and the peripheral wallmore laterally than axially, wherein a portion of the wall of thepre-combustion chamber extends into the ovoid bowl, and the portion ofthe ovoid bowl extends circumferentially around a portion of the wall ofthe pre-combustion chamber when the piston is configured proximal a topdead center position.
 21. The engine of claim 20, wherein a portion ofthe wall of the pre-combustion chamber is configured to partly extendinto the ovoid bowl when the piston is near top dead center.
 22. Theengine of claim 20, wherein the ovoid bowl wall is configured to receivea flame ejected from the jet apertures and travelling along a peripheryof the cylinder head, and redirect a portion of the flame such thatair/fuel mixture in the main combustion chamber proximal the ovoid bowlwall is ignited by the portion, and then air/fuel mixture proximal acentral region of the main combustion chamber is ignited by flameproximal the ovoid bowl wall.
 23. The engine of claim 20, wherein eachof the passages has a width, and each of the passages has a length thatis at least an order of magnitude greater than the width.
 24. The engineof claim 20, wherein the jet apertures of the plurality of passages arearranged radially.
 25. The engine of claim 20, wherein the jet aperturesof the plurality of passages are arranged to direct flame ejected frompre-combustion chamber through the plurality of passages orthogonal tothe cylindrical wall.
 26. The engine of claim 20, further comprising apressure sensor configured to provide a pressure signal representativeof a fluid pressure in the pre-combustion chamber and fluid pressure inthe main combustion chamber.
 27. The engine of claim 26, furthercomprising a controller configured to adjust activation of the igniterbased on the pressure signal such that CA50 to CA90 is shorter then CA10to CA50.
 28. The engine of claim 26, further comprising a controllerconfigured to adjust activation of the igniter based on the pressuresignal such that about 85% of heat release (HR) occurs by about 20degrees after top dead center.
 29. The engine of claim 20, wherein thejet aperture is configured to direct fluid flow from the passage along aperiphery of the cylinder head and away from a center of the ovoid bowl.30. The engine of claim 20, wherein the jet aperture is configured todirect the fluid flow along a trajectory that is substantiallyorthogonal to a center axis of the pre-combustion chamber.
 31. Theengine of claim 30, wherein the trajectory is at an angle between +30degrees and −30 degrees away from orthogonal to the center axis of thepre-combustion chamber.
 32. The system of claim 9, wherein the jetaperture is configured to direct fluid flow from the passage along aperiphery of the cylinder head and away from a center of the ovoid bowl.33. The system of claim 9, wherein the jet aperture is configured todirect the fluid flow along a trajectory that is substantiallyorthogonal to a center axis of the pre-combustion chamber.
 34. Thesystem of claim 33, wherein the trajectory is at an angle between +30degrees and −30 degrees away from orthogonal to the center axis of thepre-combustion chamber.
 35. The method of claim 1, wherein directing theflame to eject the pre-combustion chamber through the plurality ofpassages in the wall of the pre-combustion chamber proximal to thecylinder head away from the center of the ovoid bowl, toward the gap andthe portion of the ovoid bowl wall adjacent the face comprises directingthe flame to eject the pre-combustion chamber through the plurality ofpassages in the wall of the pre-combustion chamber, along the peripheryof the cylinder head and away from the center of the ovoid bowl towardthe peripheral wall.
 36. The method of claim 1, wherein directing theflame to eject the pre-combustion chamber through the plurality ofpassages in the wall of the pre-combustion chamber proximal to thecylinder head away from the center of the ovoid bowl, toward the gap andthe portion of the ovoid bowl wall adjacent the face comprises directingthe flame to eject the pre-combustion chamber through the plurality ofpassages in the wall of the pre-combustion chamber, toward the wallalong a trajectory that is substantially orthogonal to a center axis ofthe pre-combustion chamber.
 37. The method of claim 1, wherein directingthe flame to eject the pre-combustion chamber through the plurality ofpassages in the wall of the pre-combustion chamber proximal to thecylinder head away from the center of the ovoid bowl, toward the gap andthe portion of the ovoid bowl wall adjacent the face comprises directingthe flame to eject the pre-combustion chamber in a radially outwardpattern away from a center axis of the main combustion chamber throughthe plurality of passages in the wall of the pre-combustion chamberproximal to the cylinder head, toward the peripheral wall.